In a chronograph with an instantaneous or semi-instantaneous minute counter, the minute counter wheel is independent of the other gear trains of the watch and only has tension during the short period when the minute-counter finger is advancing the minute-counter train. The role of the minute-counter jumper is to keep the minute-counter wheel stationary at all other times and to position the wheel so that the hand can align consistently with the markers on the dial.
The positioning of the jumper spring is usually adjustable with an eccentric post. The spring will position the wheel such that two teeth maintain contact with the spring when there is no tension. It is important that the wheel maintain the same position when the reset-to-zero hammer is in contact with the heart cam of the minute counter. The position of the spring should be adjusted when the hammer is against the cam. When the hammer lifts away from the heart cam, the wheel can shift slightly due to sideshake but should not rotate due to the tension of the jumper. The tension of the spring needs to be sufficient enough to prevent movement of the hand when the watch receives a shock, to limit its advance to a single tooth when it receives an impulse from the minute finger, but weak enough that it does not significantly impact amplitude during the advance of the counter.
In the ETA 7750, the base of the spring should be flat, flush to the edge of the chronograph bridge, and the eccentric post should be in the slot. Be sure to use the correct tool when adjusting the eccentric.
